The invention relates to cylinder ampoules of the type comprising a tubular vessel having a first end with a membrane sealingly closing this first end, and a second end closed by a piston which can be forced into the tube to press out a liquid, e.g. a medicine, stored in said tube between said piston and the membrane when an injection needle is mounted piercing the membrane.
This type of ampoule or cartridge is used in various types of syringes and manual or automatic medication apparatuses. The syringe may either be of a durable type, where the user changes the ampoule when it is empty, or they may be disposable in which case the ampoule is mounted in the syringe by the manufacturer and the whole device including the ampoule is disposed of when the ampule is empty. In automatic medication apparatuses the ampoule may be changed when it is empty or it may be a part of a disposable part comprising parts of the apparatus which have to be changed frequently, e.g., an infusion needle, a catheter, batteries etc. This way it is ensured that these parts are changed at least each time the ampoule is replaced.
In pen shaped syringes, it is desirable that the piston in the ampoule is blocked against backward movement when it has been pressed forward in the ampoule to press out a dose of medicine through a needle mounted at the neck end of the ampoule. Immediately after an injection has been made by pressing home an injection button, an internal pressure exists in the ampoule due to the elasticity of the piston and the flow resistance in the needle. This pressure subsides when the liquid has passed out through the needle and is absorbed in the tissue. However, if the pressure on the injection button is released before such an absorption is finished, the pressure in the ampoule will press the piston backward to relieve this pressure and the full set dose will not be injected.
Blocking of the piston against such backward movement is commonly obtained by providing a piston rod, through which the pressure is transmitted from the injection button to the piston, with teeth which are engaged by a pawl provided in the housing of the syringe. EP 327 910 describes a syringe for insulin injection by which the teeth on the piston rod each has a length corresponding to the distance the piston has to be advanced to obtain the injection of the minimal dose which can be set. I.e. the blocking of the piston against movement in a backward direction takes place in steps. A continuously acting blocking is obtained in the syringe described in WO 92/12747 wherein the blocking is performed by a sharp edged leaf spring which is mounted in the syringe housing and engages a smooth piston rod at an acute angle so that the piston rod may be passed forward to press the piston into the ampoule whereas an attempt to pass the piston rod backward will make the sharp edges of the leaf spring cut into the piston rod to stop further backward movement. If this analogue detent mechanism is used in syringes of the durable type the cutting marks which the leaf spring makes in the piston rod will soon make this piston rod appear rather as a toothed than a smooth rod.
It is an object of the invention to provide an ampoule of the kind described in the opening of this application and by which the detent blocking the piston against backward movement is attached to the disposable ampoule instead of relying on parts of the injection mechanism of the syringe.
This is obtained by an ampoule of the kind mentioned which is according to the invention characterised in that the ampoule tube is made from a plastically deformable material and that a pressure foot on which a piston rod is acting abuts an outer end of the piston and carries a spring plate which is mainly perpendicular to the ampoule axis and has at least one diameter which is larger than the inner diameter of the ampoule and where edges of the plate abutting the inner wall of the ampoule are deflected away from the piston to form an acute angle with said wall.
According to the invention the spring plate may be made of a harder material than is the ampoule, preferably from an elastic metal.
The parts of the spring plate abutting the inner wall of the ampoule may, due to the direction of their deflection, slide over the wall when the piston is pressed inwardly in the ampoule. If the piston attempts to move outwardly in the ampoule, the edges of the spring plate abutting the ampoule wall will cut into this wall and stop any outward movement of the piston. The cut marks left by the cutting edges of the spring plate in the wall of the ampoule will in all cases be disposed of when the ampoule is empty. Consequently, the cut marks will not be detrimental to the functioning of a new ampoule which replaces the used one. As the retraction detent is always positioned immediately behind the piston, a minimal tolerance is obtained insofar as the influence of the elasticity of the piston rod will not be added to the influence of the elasticity of the piston.
In an embodiment of the cylinder ampoule according to the invention the spring plate may be integral with the pressure foot. Further the piston rod may be integral with the pressure foot so that the piston, the spring plate, the pressure foot, and the piston rod forms an integral unit.
In another embodiment of the invention the spring plate is a rectangular leaf spring plate extending through a slot in the pressure foot and having diagonals which are longer that the inner diameter of the ampoule. The corners of the plate at the ends of the diagonals are deflected away from the piston towards the open end of the ampoule to form an acute angle with the ampoule wall when the pressure foot is pressed into the end of the ampoule to abut the piston. This construction allow the pressure foot to be moved inward in the ampoule by which movement the deflected corners will slide over the wall whereas an attempt to move the pressure foot outward will make the corners of the leaf spring plate bite into the wall of the ampoule to block any outward movement of the pressure foot.
Another object of the invention is to provide a rotation detent which prevents rotation relative to the ampoule. Such a rotation detent may be obtained by splitting up the spring plate so that the engagement between this plate and the ampoule wall takes place in a number of circumferentially spaced points or zones of the ampoule wall. When the plate cuts into the ampoule wall in such spaced zones the engaging parts of the plate have to force their ways through the parts of the ampoule wall separating the points or zones of engagement if the plate shall be rotated. This will yield a considerable resistance against rotational movement of the plate relative to the ampoule and elements coupled to the plate in a way preventing relative rotation of these elements and the plate will also be prevented from rotation relative to the ampoule.
Further according to the invention the ampoule may have an extension extending beyond the piston when the ampoule is full. This extension may surround the piston rod over the entire length of this rod.
The piston rod may be provided with an outer thread and the full ampoule may be extended behind the piston to surround the piston rod over its entire length. Provided with the features, the ampoule may form a main part of a pen shaped syringe, the syringe further comprising a dose setting and injection means cooperating with the piston rod and a cap covering at least a part of the ampoule and its extension. Such a syringe can be disposed of when the ampoule is empty.
According to an embodiment of the invention, the extension of the ampoule may on its inner wall be provided with a protrusion which cooperates with the dose setting and injection means to provide an audible and tactile indication of the setting of a dose and a stop defining the maximum dose which can be set.
Further, according to an embodiment of the invention, the extension at the transition from the ampoule to said extension is, along its perimeter, provided with equidistant axial recesses engaged by an axial spline at the inner wall of the cap, to block against relative rotation of the ampoule and the cap during the operation of the dose setting member. By this construction, the ampoule is rotationally fixed in the cap, and rotating the dose setting means relative to the cap causes the dose setting means to rotate relative to the ampoule and the piston rod.
According to still another embodiment of the cylinder ampoule according to the invention, an end edge of the extension is provided with a toothing comprising teeth having an abrupt leading edge and a ramp shaped trailing edge, which toothing cooperates with a corresponding toothing on an edge of a dose setting and injection button. By said toothings, it is ensured that the dose setting and injection button from its zero point can only be rotated in a direction by which a positive dose is set.
According to another embodiment of the invention, the cap fits over the ampoule and its extension and may abut the dose setting and injection button. The cap may have a recess in its abutting edge and a scale along this edge. The injection button has on its abutting edge a projection fitting into the recess in the injection button. When the cap is mounted with the protrusion on the dose setting and injection button engaging the recess of the cap, it is ensured that a marker on said protrusion points at the zero on a scale on the outer perimeter of the cap.